In the Cave stands the Molecular-Fusion-Generator, which is the power supplier for the Time Riders.
The Molecular-Fusion-Generator sets an uncalculatable amount of energy free due to its nuclear reactions. Only a very strong concentrated amount of that energy will open the possibility for the Time Riders to travel through space and time. The produced heat is shot through a perfectly symmetric crystal, that causes concentric waves to produce wormholes in the time. The resulting electromagnetic field allows the Time Riders to get to the speeds where it can move freely through the tunnels.
